The DVD based Mk4 is nice and hackable. I upgraded my E46 M3 from the Mk3 CD based system, to MK4, updated firmware to enable 3D maps, camera locations, extended VDO POI search, 7 digit Postcode and a nice ///M logo upon startup. In addition I added the outstanding Intravee 2 iPod integration, which gave OEM look and feel to the iPod interface on the MK4 and enabled steering wheel key mapping and Sat based clock updates, amongst other things.
I've not touched the HDD based CIC system in the E92...